stdlib/test-bz22786: Avoid spurious test failures using alias mappings

On systems without enough random-access memory, stdlib/test-bz22786
will go deeply into swap and time out, even with a substantial
TIMEOUTFACTOR.  This commit adds a facility to construct repeating
strings with alias mappings, so that the requirement for physical
memory, and uses it in stdlib/test-bz22786.

1 files changed, 278 insertions, 0 deletions

diff --git a/support/blob_repeat.c b/support/blob_repeat.c
new file mode 100644
index 0000000000..da4ca83043
--- /dev/null
+++ b/support/blob_repeat.c
@@ -0,0 +1,278 @@
+/* Repeating a memory blob, with alias mapping optimization.
+   Copyright (C) 2018 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <string.h>
+#include <support/blob_repeat.h>
+#include <support/check.h>
+#include <support/support.h>
+#include <support/temp_file.h>
+#include <support/xunistd.h>
+#include <sys/mman.h>
+#include <unistd.h>
+#include <wchar.h>
+
+/* Small allocations should use malloc directly instead of the mmap
+   optimization because mappings carry a lot of overhead.  */
+static const size_t maximum_small_size = 4 * 1024 * 1024;
+
+/* Internal helper for fill.  */
+static void
+fill0 (char *target, const char *element, size_t element_size,
+       size_t count)
+{
+  while (count > 0)
+    {
+      memcpy (target, element, element_size);
+      target += element_size;
+      --count;
+    }
+}
+
+/* Fill the buffer at TARGET with COUNT copies of the ELEMENT_SIZE
+   bytes starting at ELEMENT.  */
+static void
+fill (char *target, const char *element, size_t element_size,
+      size_t count)
+{
+  if (element_size == 0 || count == 0)
+    return;
+  else if (element_size == 1)
+    memset (target, element[0], count);
+  else if (element_size == sizeof (wchar_t))
+    {
+      wchar_t wc;
+      memcpy (&wc, element, sizeof (wc));
+      wmemset ((wchar_t *) target, wc, count);
+    }
+  else if (element_size < 1024 && count > 4096)
+    {
+      /* Use larger copies for really small element sizes.  */
+      char buffer[8192];
+      size_t buffer_count = sizeof (buffer) / element_size;
+      fill0 (buffer, element, element_size, buffer_count);
+      while (count > 0)
+        {
+          size_t copy_count = buffer_count;
+          if (copy_count > count)
+            copy_count = count;
+          size_t copy_bytes = copy_count * element_size;
+          memcpy (target, buffer, copy_bytes);
+          target += copy_bytes;
+          count -= copy_count;
+        }
+    }
+  else
+    fill0 (target, element, element_size, count);
+}
+
+/* Use malloc instead of mmap for small allocations and unusual size
+   combinations.  */
+static struct support_blob_repeat
+allocate_malloc (size_t total_size, const void *element, size_t element_size,
+                 size_t count)
+{
+  void *buffer = malloc (total_size);
+  if (buffer == NULL)
+    return (struct support_blob_repeat) { 0 };
+  fill (buffer, element, element_size, count);
+  return (struct support_blob_repeat)
+    {
+      .start = buffer,
+      .size = total_size,
+      .use_malloc = true
+    };
+}
+
+/* Return the least common multiple of PAGE_SIZE and ELEMENT_SIZE,
+   avoiding overflow.  This assumes that PAGE_SIZE is a power of
+   two.  */
+static size_t
+minimum_stride_size (size_t page_size, size_t element_size)
+{
+  TEST_VERIFY_EXIT (page_size > 0);
+  TEST_VERIFY_EXIT (element_size > 0);
+
+  /* Compute the number of trailing zeros common to both sizes.  */
+  unsigned int common_zeros = __builtin_ctzll (page_size | element_size);
+
+  /* In the product, this power of two appears twice, but in the least
+     common multiple, it appears only once.  Therefore, shift one
+     factor.  */
+  size_t multiple;
+  if (__builtin_mul_overflow (page_size >> common_zeros, element_size,
+                              &multiple))
+    return 0;
+  return multiple;
+}
+
+/* Allocations larger than maximum_small_size potentially use mmap
+   with alias mappings.  */
+static struct support_blob_repeat
+allocate_big (size_t total_size, const void *element, size_t element_size,
+              size_t count)
+{
+  unsigned long page_size = xsysconf (_SC_PAGESIZE);
+  size_t stride_size = minimum_stride_size (page_size, element_size);
+  if (stride_size == 0)
+    {
+      errno = EOVERFLOW;
+      return (struct support_blob_repeat) { 0 };
+    }
+
+  /* Ensure that the stride size is at least maximum_small_size.  This
+     is necessary to reduce the number of distinct mappings.  */
+  if (stride_size < maximum_small_size)
+    stride_size
+      = ((maximum_small_size + stride_size - 1) / stride_size) * stride_size;
+
+  if (stride_size > total_size)
+    /* The mmap optimization would not save anything.  */
+    return allocate_malloc (total_size, element, element_size, count);
+
+  /* Reserve the memory region.  If we cannot create the mapping,
+     there is no reason to set up the backing file.  */
+  void *target = mmap (NULL, total_size, PROT_NONE,
+                       MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+  if (target == MAP_FAILED)
+    return (struct support_blob_repeat) { 0 };
+
+  /* Create the backing file for the repeated mapping.  */
+  int fd;
+  {
+    char *temppath;
+    fd = create_temp_file ("support_blob_repeat-", &temppath);
+    if (fd < 0)
+      FAIL_EXIT1 ("create_temp_file: %m");
+    xunlink (temppath);
+    free (temppath);
+  }
+
+  /* Make sure that there is backing storage, so that the fill
+     operation will not fault.  */
+  if (posix_fallocate (fd, 0, stride_size) != 0)
+    FAIL_EXIT1 ("posix_fallocate (%zu): %m", stride_size);
+
+  /* The stride size must still be a multiple of the page size and
+     element size.  */
+  TEST_VERIFY_EXIT ((stride_size % page_size) == 0);
+  TEST_VERIFY_EXIT ((stride_size % element_size) == 0);
+
+  /* Fill the backing store.  */
+  {
+    void *ptr = mmap (target, stride_size, PROT_READ | PROT_WRITE,
+                      MAP_FIXED | MAP_FILE | MAP_SHARED, fd, 0);
+    if (ptr == MAP_FAILED)
+      {
+        int saved_errno = errno;
+        xmunmap (target, total_size);
+        xclose (fd);
+        errno = saved_errno;
+        return (struct support_blob_repeat) { 0 };
+      }
+    if (ptr != target)
+      FAIL_EXIT1 ("mapping of %zu bytes moved from %p to %p",
+                  stride_size, target, ptr);
+
+    /* Write the repeating data.  */
+    fill (target, element, element_size, stride_size / element_size);
+
+    /* Return to a PROT_NONE mapping, just to be on the safe side.  */
+    ptr = mmap (target, stride_size, PROT_NONE,
+                MAP_FIXED | MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+    if (ptr == MAP_FAILED)
+      FAIL_EXIT1 ("Failed to reinstate PROT_NONE mapping: %m");
+    if (ptr != target)
+      FAIL_EXIT1 ("PROT_NONE mapping of %zu bytes moved from %p to %p",
+                  stride_size, target, ptr);
+  }
+
+  /* Create the alias mappings.  */
+  {
+    size_t remaining_size = total_size;
+    char *current = target;
+    int flags = MAP_FIXED | MAP_FILE | MAP_PRIVATE;
+#ifdef MAP_NORESERVE
+    flags |= MAP_NORESERVE;
+#endif
+    while (remaining_size > 0)
+      {
+        size_t to_map = stride_size;
+        if (to_map > remaining_size)
+          to_map = remaining_size;
+        void *ptr = mmap (current, to_map, PROT_READ | PROT_WRITE,
+                          flags, fd, 0);
+        if (ptr == MAP_FAILED)
+          {
+            int saved_errno = errno;
+            xmunmap (target, total_size);
+            xclose (fd);
+            errno = saved_errno;
+            return (struct support_blob_repeat) { 0 };
+          }
+        if (ptr != current)
+          FAIL_EXIT1 ("MAP_PRIVATE mapping of %zu bytes moved from %p to %p",
+                      to_map, target, ptr);
+        remaining_size -= to_map;
+        current += to_map;
+      }
+  }
+
+  xclose (fd);
+
+  return (struct support_blob_repeat)
+    {
+      .start = target,
+      .size = total_size,
+      .use_malloc = false
+    };
+}
+
+struct support_blob_repeat
+support_blob_repeat_allocate (const void *element, size_t element_size,
+                              size_t count)
+{
+  size_t total_size;
+  if (__builtin_mul_overflow (element_size, count, &total_size))
+    {
+      errno = EOVERFLOW;
+      return (struct support_blob_repeat) { 0 };
+    }
+  if (total_size <= maximum_small_size)
+    return allocate_malloc (total_size, element, element_size, count);
+  else
+    return allocate_big (total_size, element, element_size, count);
+}
+
+void
+support_blob_repeat_free (struct support_blob_repeat *blob)
+{
+  if (blob->size > 0)
+    {
+      int saved_errno = errno;
+      if (blob->use_malloc)
+        free (blob->start);
+      else
+        xmunmap (blob->start, blob->size);
+      errno = saved_errno;
+    }
+  *blob = (struct support_blob_repeat) { 0 };
+}